1. Field of the Invention
The present invention relates to a battery pack and an electric tool.
2. Description of Related Art
In a cordless electric tool, a battery as a power supply is further required to be high in capacity and reduced in weight. To cope with this, a lithium battery whose output density is high is being expected, and is gradually employed recently.
On the other hand, when the overcharge, overdischarge, overcurrent occurs in a lithium battery, there is raised a fear of ignition in the worst case due to degradation of battery or temperature rise of battery. Accordingly, Japanese Patent Application Publication No. 06-141479 discloses a battery charger includes a protection circuit for observing the overcharge, overdischarge, overcurrent of respective cells in a battery pack. In this battery charger, if the battery voltage of the respective battery cells is lower or higher than a predetermined voltage value, and a current flowing through the battery cells is larger than a predetermined current, the protection circuit outputs a detection signal to shut off charge and discharge paths. In this way, a countermeasure for the safety, that is, preventing the overvoltage, overdischarge, overcurrent is performed.